1. Field of the Invention
The present invention is directed to the field of vehicle transmissions and more particularly to an apparatus and method of providing a continuous flow of discharge transmission fluid from a torque converter to a cooler of the transmission such that oil flow to the cooler begins at engine start up and wherein the apparatus includes a safety bypass valve that directs discharge from the torque converter directly to a lube circuit other than the cooler circuit in the event pressure within the cooler circuit rises above a predetermine pressure due to a gelling of lubricant oil or other clogging of the cooler circuit.
2. Brief Description of the Related Art
In some models of vehicles, lubricant oil flow through an automatic transmission is controlled such that, until a temperature of the oil or transmission fluid reaches a predetermined temperature after vehicle start up, the oil is allowed to bypass a cooler circuit associated with the automatic transmission. By way of example, transmissions of the Ford® 5R55 series such as the W, S and N models, are provided with a cooler bypass valve controlled by a thermostatic switch as original operating equipment. Such a thermostatically controlled valve is a directional flow control valve having a valve body that moves so as to either prevent or allow flow of oil from a transmission torque converter to the cooler circuit. Essentially, the thermostatic switch includes a piston which shifts the valve from a first position, to block flow to the cooler circuit when the temperature of the oil is below a predetermine temperature so that all oil is directed to a lube circuit of the transmission, to a second position when the oil temperature is above the predetermined temperature so that the oil is directed toward the cooler circuit. At low temperatures, the bypass valve is urged by a spring to close an outlet to prevent flow to the cooler circuit, however, as the temperature rises to approximately 160° F., the thermostat urges the valve against the spring pressure such that heated oil is directed to the cooler circuit.
It has been determined that the thermostatic bypass valve assembly may fail to operate to open the bypass valve until temperatures of the transmission fluid or oil become damagingly high causing failure or lock up of the gears of the transmission. In the event of failure of the bypass valve to open in a proper manner, the overdrive sun and planet gears are normally the first gears to be adversely effected as they generally receive the least amount of oil flow during engine operation.
In addition to the foregoing, under normal operating conditions, the Ford® transmissions identified above are designed to provide maximum flow of approximately 0.7 gallons of lubricant in 20 seconds to the cooling circuit when the bypass valve is opened to direct flow to the cooling circuit. As only a small amount of the cooled lubricant is directed to the overdrive planetary gears, any overheating caused by failure of the cooler bypass valve or a delay in opening of the cooler bypass valve to the cooler circuit will have a generally immediate effect on such gears.
In view of the foregoing, there is a need to prevent potential damage that may be caused to vehicle transmissions due to failure or faulty operation of thermostatically controlled bypass valves. There is also a need to increase the quantity of lubrication fluid flow to the overdrive sun and planetary gears to ensure that such gears are not easily damaged upon heat build up.